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LANDSLIDE AND ROCKERY WALL MONITORING SYSTEM FOR
RESIDENTIAL AREALaura Y. Coiffe, Diplôme d‘Ingénieur
William F. Kane, PhD, PG, PEKANE GeoTech, Inc.
Stockton, California
Honolulu, Hawaii
18th Annual Technical Forum
Geohazards Impacting Transportation in Appalachia
August 7 to 9, 2018
Baltimore, MD
OVERVIEW
Landslides• Nature of failures
Rockery Walls• What is a rockery wall?• Why rockery wall can present a potential risk?
Case Study• Nature of the hazards• Repair of the slope• Monitoring movement of wall
What are the optimal monitoring solutions for the case study?• Monitoring the slope after the repair• Monitoring the rockery wall• Data Acquisition
LANDSLIDES
Nature of failures:Soil saturationSlope angleSurchargeGround water
WHAT IS A ROCKERY WALL?
Difficult design Not standardized
Construction relies on installers’ skill No reinforcement Can fail due to soil movement behind the
wall
HAZARDS OF A ROCKERY WALL
CASE STUDY : RESIDENTIAL AREA IN NEVADA
NATURE OF THE HAZARDS –LANDSLIDE
Head Scarp Undocumented Fill
NATURE OF THE HAZARDS –ROCKERY WALL
REPAIR OF THE SLOPE
SOLUTION - MONITORING
Monitoring the slope Monitoring the boulders
SLOPE INSTRUMENT LAYOUT
TDR
TDR
TDR
TDR
TDRTDR
IPI/Probe InclinometerVWP
VWP
Base Station (ADAS)
TIME-DOMAIN REFLECTOMETRY (TDR) : HOW IT WORKS
Works like radar Reflectometer transmits short rise-
time pulse Pulse is transmitted along the cable
• Cable has a characteristic velocity of propagation (Vp).
• Vp is known as a percentage of the speed of light.
Pulse if reflected and the travel time determined• Length of the sensor cable can be calculated
TIME-DOMAIN REFLECTOMETRY
Severity of and distance to reflection is determined
Electrical pulse sent down cable
Pulse reflected at crimps and breaks
Coaxial cable grouted into borehole
MONITORING THE SLOPE AFTER REPAIR : TIME-DOMAIN REFLECTOMETRY
VIBRATING WIRE PIEZOMETER
Monitors pore-water pressure in soilWater pressure changes the
tension in the wire
MONITORING THE SLOPE AFTER REPAIR : VIBRATING
WIRE PIEZOMETER
ROCKERY WALL INSTRUMENTATION LAYOUT
Base Station (ADAS)
MONITORING OF THE ROCKERY WALL : VIBRATING WIRE TILTMETER
8 Uniaxial tiltmeters on 3 different levels
All connected to a vibrating wire analyzer
AUTOMATED DATA ACQUISITION SYSTEM
Instruments connected to a datalogger Datalogger collects data Real-Time monitoring Email alerts sent via modem
WEB-PAGE INTERFACE
Station Monitoring
Shear Key Rockery Wall
CONCLUSIONS
Post-construction monitoring is essentialMonitoring can determine if a problem actually existsWide variety of instrumentation is availableAutomated instrumentation is cost-effective
• Can be reused after stabilization is assured• Relatively inexpensive• Allows real-time data acquisition to spot trends